20/20 or 6/6 Vision
20/20 vision describes the sharpness of a person’s vision 20 feet from a vision chart. In Australia as we use the metric system, which means 20/20 is 6/6 vision. 20 feet equates to six meters.
To test your sight, your optometrist will have you sit 6 metres away from a wall-mounted vision chart and cover one eye at a time while you attempt to read all the letters on the chart. If you can read all the letters successfully down to the 6th line then you have 6/6 or 20/20 vision. People with low vision will be able to read less of the chart at the standard distance.
The clarity of your sight is the standard test, but your optometrist will take into consideration other aspects of vision such as your peripheral vision, depth and colour perception, and focusing ability. All of these factors contribute to your sight.
Your optometrist will also check to ensure that your eyes are working together and assess your ability to focus for near vision. The internal and external structures of your eyes will be carefully examined. Special instruments are used so that your optometrist can assess your eyes under high magnification, with special optical filters and in 3-D. Assessments of the pressure of the eyeball, fields of view and colour vision may also be done.
Your eyes will be examined for signs of cataract, glaucoma or macular degeneration, or other diseases such as high blood pressure or diabetes that may be causing your low vision. Sometimes medication you are taking can have side effects that can affect your eye health.
Optometrists provide ongoing support and regular appointments will keep a check on the effectiveness of the aids you have and make any necessary adjustments.